JSONP 核心原理：script 标签不受同源策略约束，所以可以用来进行跨域请求，优点是兼容性好，但是只能用于 GET 请求；

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1const jsonp = ({ url, params, callbackName }) => {
2    const generateUrl = () => {
3        let dataSrc = ''
4        for (let key in params) {
5            if (params.hasOwnProperty(key)) {
6                dataSrc += `${key}=${params[key]}&`
7            }
8        }
9        dataSrc += `callback=${callbackName}`
10        return `${url}?${dataSrc}`
11    }
12    return new Promise((resolve, reject) => {
13        const scriptEle = document.createElement('script')
14        scriptEle.src = generateUrl()
15        document.body.appendChild(scriptEle)
16        window[callbackName] = data => {
17            resolve(data)
18            document.removeChild(scriptEle)
19        }
20    })
21}